RegExLib.com bills itself as the Internet's first Regular Expression Library. It has an online tool for testing regular expressions.

The Regex Coach

Content formatting with Regexes

The Regex Coach a graphical application for Linux and Windows which can be used to experiment with (Perl-compatible) regular expressions interactively.

weitz.de/regex-coach.

HREF URL Extractor

Working with regular expressions

To extract the value (URL) of an HREF attribute from a string, use the preg_match or preg_match_all function. This example use preg_match_all to find all the matches.

preg_match_all - Perform a global regular expression match

preg_match_all (pattern (string), target (string), matches (array), optional flags)

Searches target for all matches to the regular expression given in pattern and puts them in matches in the order specified by the flags.

The regular expression: <\s*a\s+[^>]*href\s*=\s*[\"']?([^\"' >]+)[\"' >]